Isolation and identification of bioactive secondary metabolites from Salinispora arenicola obtained from ocean sediments from the Madeira Archipelago

Abstract

Recently there has been an increase in pathogenic microorganisms resistant to antibiotics, infectious diseases and the appearance of new threats to human health and the economy. The inability of terrestrial natural product-based drugs to solve these problems has led scientists to look at unexplored habitats in search of new drugs. The marine environment has established itself as a remarkably rich treasure of new bioactive compounds with a wide range of biological properties, including antimicrobial, anti-fungal, anti-cancer, anti-inflammatory and cytotoxic. In the short time the marine environment has been explored, its bioprospecting has resulted in the approval of seven drugs, withcurrently 23 compounds in clinical trials and hundreds in the pre-clinical pipeline. In this work, a bioassay-guided approach was used to study the bioactive secondary metabolites of the Salinispora arenicola strain PTM-99 collected from oceanic sediments off the coast of the Madeira archipelago. Chromatographic techniques, such as flash chromatography and High Performance Liquid Chromatography (HPLC), were used for the isolation and purification of secondary metabolites. About 52 compounds were isolated from a resulting culture of 7 days of incubation and 82 were isolated from a culture of 14 days of incubation (counting the F8-F9 fraction compounds). The 7-day-old culture was tested for antibacterial activity against pathogenic bacteria Enterococcus faecium VRE EF82 resistant to vancomycin and Staphylococcus aureus resistant to methicillin MRSA COL, having 20 compounds revealed activity. The compounds exhibited antibacterial activity in the range of MIC 250 to 62.5 μg/ml. Bioactive and other relevant compounds were structurally analyzed through spectroscopic methods including one-dimensional and two-dimensional Nuclear Magnetic Resonance experiments, ultraviolet, Infra-red and the non-spectroscopic method specific optical rotation. It was found that most of the compounds isolated contain lactam core, piperazine core and/or aromatic backbone. Two known diketopiperazines are reported for the first time from the Salinispora genus. Two macrolides are currently being structurally elucidated.